1. Technical Field
The present invention relates to an ink jet printer that forms predetermined characters and images by ejecting ink droplets of, for example, a plurality of colors through a plurality of nozzles to form particles (ink dots) on a printing medium.
2. Related Art
As a personal computer or a digital camera has come in to wide use, such an ink jet printer has been widely used in an office and home because the ink jet printer is cheap and can print a high-quality of a color image in general.
In such an ink jet printer, while reciprocating in a direction intersecting a transport direction of the printing medium, a moving unit called a carriage that has an ink cartridge and a printing head generally ejects ink droplets through the nozzles of the printing head and forms ink dots on the printing medium in order to obtain desired characters or images. In addition, the carriage includes ink cartridges of four colors (yellow, magenta, cyan, and black) and the printing heads of the colors. Accordingly, the ink jet printer can perform a mono-color printing operation and also perform a full-color printing operation (where in addition to the four colors, light cyan, and light magenta, ink cartridges of 6 colors, 7 colors, or 8 colors are available).
In the ink jet printer that performs the printing operation while reciprocating the ink jet head of the carriage in the direction intersecting the transport direction of the printing medium, the ink jet heads have to reciprocate 10 or more times in order to print an image of an one-page. In contrast, in an ink jet printer having a longitudinal ink jet head (which does not need to be an incorporated unit) of which the size is the same as the width of the printing medium and having no carriage, it is not necessary to move the ink jet head in a transverse direction of the printing medium and the printing operation is possible by passing the printing medium just once. Therefore, a high-speed printing operation is possible. In general, the ink jet printer of the former type is called “a multi-pass (serial) type ink jet printer” and the ink jet printer of the latter type is called “a line head type ink jet printer”. In particular, the line head type ink jet printer allows a transport belt to absorb the printing medium by electrostatic absorption, air absorption, or the like in order to transport the printing medium.
Such a method of transporting the printing medium is particularly effective in the line head type ink jet printer. In an ink jet printer disclosed in JP-A-2005-75475, line head type ink jet heads are disposed upstream and downstream in a transport direction of a printing medium, a plurality of transport belts are disposed in a direction intersecting the transport direction of the printing medium at a predetermined interval, the printing medium is electrostatically absorbed on the transport belts to be transported, ink droplets are ejected on the transported printing medium from the ink jet heads disposed upstream and downstream. The ink jet heads are disposed at spaces between the transport belts and cleaning units directly below the ink jet heads perform a so-called cleaning operation in order to clean, for example, nozzles of the ink jet heads.
However, in order for such an ink jet printer to print a high-quality image, the ink droplets have to be ejected on an exact target position of the printing medium. Accordingly, a distance (gap) between the nozzle surface of the ink jet heads and the surface of the printing medium has to be uniform. However, when the printing medium is transported by the plurality of transport belts described above, the end portions (which are the end portions of the printing medium in the transverse direction of the printing medium when the transport direction of the printing medium refers to a longitudinal direction and a direction interesting the direction of the printing medium refers to a transverse direction) of the printing medium which is not loaded on the transport belt in the direction intersecting the transport direction of the printing medium droops. Then, the distance between the nozzle surface of the ink jet heads and the surface of the printing medium may be changed. In order to solve this problem, an ink jet printer disclosed in JP-A-2005-88329 is configured so that support members each having a plurality of plate-like members are disposed between the plurality of transport belts, portions of the plate-like members upstream side in the transport direction of the printing medium are chamfered, and the end portions of the transported printing medium in the direction intersecting the transport direction of the printing medium, that is, the drooping end portions are lifted by the chamfered plate-like members.
However, in the ink jet printer disclosed in JP-A-2005-88329, for example, all the chamfered portions of the plurality of plate-like members are of the same size. Therefore, the end portions of the transported printing medium in the direction intersecting the transport direction almost simultaneously come in contact with the plurality of plate-like members constituting the support members. However, since the endmost portions of the transported printing medium in the direction intersecting the transport direction further droop, the more drooping end portions of the printing medium in the direction intersecting the transport direction may not be placed on the chamfered portions of the plate-like members, but may collide with portions below the chamfered portions. If the end portions of the printing medium in the direction intersecting the transport direction collide with the plate-like members in this manner, transport failure, so-called paper-sheet jam may occur. This problem can frequently occur in the printing medium with low rigidity or the printing medium of which the rigidity is reduced due to ink absorbed by the printing medium.